The present invention is directed toward a thwartable link for a vertical line and more particularly, toward a thwartable or breakaway link that severs a vertical line from a series of lobster traps in order to prevent injury to a whale that may come in contact with the line.
In the commercial lobstering business, it is common practice to connect a plurality of lobster traps together utilizing a series of ropes. The lobster traps are baited, dropped to the bottom of the seabed from a fishing boat and left for several days before they are retrieved by the lobster fishermen. The position of the traps at sea is marked by a buoy connected by a rope to the first trap in the series. This rope, commonly referred to as a vertical line extends vertically upwardly from the trap to the buoy which may be a distance of one to several hundred feet. Alternatively, two buoys are sometimes used that are spaced apart from each other with the first buoy tied to the first trap in the series by a first vertical line and the second buoy tied to the last trap in the series by a second vertical line.
After the traps have been set and left for several days, the fishing boat returns and identifies its traps by its unique buoy. The traps are retrieved by pulling the vertical line upwardly onto the boat. Since the traps are tied to the vertical line, they are also pulled upwardly onto the boat. Lobsters are removed from the traps and the process is repeated.
Unfortunately, the commercial interest in keeping the traps coupled to their associated surface buoys or other markers through vertical lines can run counter to environmental interest. In particular, it is known that whales, such as the endangered right whale, come in contact with vertical lines and other man-made components of fishing equipment, occasionally with undesired outcomes. Under the 1995 Marine Mammal Protection Act, legislation was enacted to mandate that there would be no right whale deaths occurring from interaction with commercial fishing equipment. Contemplated steps for achieving that goal have included the closure of important fishing areas for extended periods of time as well as unspecified significant modifications to fishing equipment. Either option would adversely impact the commercial fishing industry, without the certainty of solving the problem. That is, the mechanism of whale entanglement with fishing equipment is unclear and therefore the existing proposed solutions may not achieve the desired goal.
It is believed that the whales may become entangled in vertical buoy lines and other equipment in the ocean by the following process. First, when they encounter such obstacles, they may move in the direction of the obstacle, such as upward along a lobster vertical line. The force of the whale's efforts pulls the buoy underwater until such time as it is captured in the whale's baleen, against a flipper, or against some other body part. As the whale moves, pulling the entire connected underwater structure with it, it likely thrashes about, becoming further entangled. This entanglement may trap the whale underwater where it drowns.
One solution devised to combat the above problem is a weak link or breakaway link. A breakaway link, as described in U.S. Pat. No. 5,913,670, is designed to be located on the unattended line. When sufficient tension is received along the line, such as the tension caused by an entangled whale, the breakaway link breaks and releases the line, allowing the whale to disentangle. The breakaway link has two major problems.
The first problem is that the tension created by reeling the line in is similar to the tension created by an entangled whale. To avoid breaking the breakaway link when reeling in the line, fishermen must locate the link close enough to the surface to reach and begin reeling in the line below the breakaway link. Often whales get caught in the line closer to the bottom of the ocean. If the line breaks only near the surface, the whales can remain entangled or become injured while disentangling even though the rope is released. The continued problem is due to the distance between the whale and the released end of the rope.
The second problem with the breakaway link is knotting. Typically, a breakaway link is some type of ring of metal. To make the link part of the unattended line, a length of rope is tied from the buoy to the link and another length of rope is tied from the link to the submerged traps. The ropes are tied to the link by making knots in the ropes. When the links break, the knots remain. Knots in the rope impede disentanglement and can cause injury to the whales. Ideally, a device should be constructed that will disengage the rope knotlessly.
A more sophisticated breakaway link is shown in U.S. Pat. No. 6,457,896 which describes a coupling that connects the buoy to the vertical line. The couple includes a notch or a reduced thickness region and may be of fixed or swivel configuration. The reduced thickness region is designed to be the primary region in contact with the connector, such as a rope. That region is designed to fail catastrophically under a selectable stress preferably greater than the stress ordinarily experienced by the coupling. For example, if the coupling is interposed between a buoy and a vertical line, the notched coupling is designed with sufficient retaining strength to remain intact when the traps are deployed and when they hauled into a boat. However, when the rope contacts a mobile underwater body, such as a whale, the strain associated with the movement of that body reaches a level that exceeds the breaking point of the coupling at the notch. At that time, the coupling breaks at the notch and the buoy is released from the rope and the lobster traps.
This solution is also unsatisfactory as it continues to suffer from the problems of the breakaway links discussed above. That is, the device is located near the buoy. As a result, the whale can still become entangled in the line under water and drown. Ideally, a device should be constructed that will disengage the rope at the bottom of an unattended line for entangled whales, but will not disengage when fishermen reel in the line.
The device shown in U.S. Pat. No. 6,928,765 attempts to solve this last problem by providing a tension activated rope severing device that is located near the bottom of the vertical line in the vicinity of the traps. However, the device shown in this patent is quite complicated. It includes a hydraulically operated damper that controls the movement of a knife blade in relation to the rope to be severed. Furthermore, it appears that there is little control over the device severing the line inadvertently when the fishermen are reeling in the line and significant tension is being applied. That is, the device may interpret the increased tension as the entanglement of a whale and sever the line.
A need, therefore, exists for a simple but effective device that is capable of releasing a vertical line from a series of lobster traps to prevent injury to whales and that is located at the bottom of the line near the traps.